1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head that irradiates near-field light on a magnetic recording medium and records data by decreasing an anisotropic magnetic field of the magnetic recording medium and to a head gimbal assembly and a magnetic recording device to which the head is used.
2. Description of the Related Art
In the field of magnetic recording using a head and a medium, further performance improvements of thin film magnetic heads and magnetic recording media have been demanded in conjunction with a growth of high recording density of magnetic disk devices. Currently, for the thin film magnetic heads, composite type thin film magnetic heads that are configured having a configuration in which a magnetoresistive (MR) element for reading and an electromagnetic transducer element for writing are laminated are widely used.
The magnetic recording medium is a discontinuous medium in which magnetic microparticles aggregate and each of the magnetic microparticles has a single magnetic domain structure. In this magnetic recording medium, one recording bit is configured with a plurality of magnetic microparticles. Therefore, in order to increase recording density, asperities at borders between adjacent recording bits need to be reduced by decreasing the size of the magnetic microparticles. However, decreasing the size of the magnetic microparticles causes a problem in that a thermal stability of magnetizations of the magnetic microparticles is decreased along with the decrease in the volume of the magnetic microparticles.
As a countermeasure against this problem, it may be considered to increase magnetic anisotropy energy Ku of the magnetic microparticles may be considered; however, the increase in Ku causes an increase in an anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, an upper limit of a writing magnetic field strength for the thin film magnetic head is substantially determined by saturation magnetic flux density of a soft magnetic material configuring a magnetic core in the head. As a result, when the anisotropic magnetic field of the magnetic recording medium exceeds an acceptable value determined from the upper limit of the writing magnetic field strength, it becomes impossible to write. Currently, as a method to solve such a problem of thermal stability, a so-called thermally-assisted magnetic recording method has been proposed in which, while a magnetic recording medium formed of a magnetic material with large Ku is used, the magnetic recording medium is heated immediately before the application of the writing magnetic field so that the writing is performed with the anisotropic magnetic field being reduced.
For this thermally-assisted magnetic recording method, a method that uses a near-field light probe, a so-called plasmon generator, which is a metal piece that generates near-field light from plasmon excited by irradiated laser light, is generally known.
A magnetic recording head disposed with a conventional plasmon generator has a configuration in which a pole that generates a writing magnetic field is disposed on a trailing side with respect to a near-field light generating portion of the plasmon generator and in which a waveguide that propagates light is disposed so as to oppose the plasmon generator. This plasmon generator couples to light propagating through the waveguide in a surface plasmon mode so as to excite surface plasmon, and the surface plasmon propagates through the plasmon generator so that the near-field light is generated at the near-field light generating portion. Furthermore, under a situation where a magnetic recording medium is heated by the near-field light generated at the near-field light generating portion of the plasmon generator and the anisotropic magnetic field of the magnetic recording medium is reduced, a writing magnetic field is applied and thereby information is written.
In the magnetic recording head having such a configuration, when a distance between the near-field light generating portion that generates the near-field light in the plasmon generator and the pole that generates the writing magnetic field is large, the strength of the magnetic field applied to the magnetic recording medium with an anisotropic magnetic field reduced by the irradiation of the near-field light becomes deficient so that it becomes difficult to write information effectively. Therefore, it is considered that making the distance between the near-field light generating portion and the pole smaller by directly contacting the pole with the plasmon generator and making a thickness of the plasmon generator thinner are effectual to write information effectively. When the thickness of the plasmon generator is thinner, the peak strength of the near-field light is decreased so that a preferred thermal assist effect may not be obtained; but, on the other hand, when the thickness of the plasmon generator is thicker, the peak strength of the near-field light can be increased, but the distance between the near-field light generating portion and the pole becomes large so that it may become difficult to write information effectively.
In contrast, in the magnetic recording head having the above-described configuration, since the magnetic field continues to be applied to the magnetic recording medium that is in a cooling process after the temperature rises by the heating, the magnetic field is further applied even to the magnetic microparticles where the magnetization has not yet stabilized after the magnetic field for recording is applied. This causes the problem that sufficient signal to noise ratio (S/N ratio) cannot be obtained in the high recording density. Therefore, in order to achieve high recording density and obtain a sufficient S/N ratio, a configuration in which a magnetic field is applied prior to heating the magnetic recording medium, i.e., a configuration in which a plasmon generator in the conventional magnetic recording head is disposed on the trailing side with respect to the pole is conceivable.
An example of the above-described magnetic recording head is a magnetic recording head provided with a plasmon generator in a shape of triangular prism that protrudes in a V-shape toward a leading side (a pole side) and a pole disposed on the leading side with respect to the plasmon generator. In the magnetic recording head having this type of configuration, the plasmon generator couples to light propagating through the waveguide in the surface plasmon mode so that the surface plasmon is excited in a V-shaped protrusion portion of the plasmon generator, and the surface plasmon propagates through the V-shaped protrusion portion of the plasmon generator. Accordingly, the waveguide is disposed on the leading side of the plasmon generator, i.e., between the plasmon generator and the pole. Therefore, the distance between the near-field light generating portion in the plasmon generator and the pole becomes large, the strength of the magnetic field applied to the magnetic recording medium with an anisotropic magnetic field reduced by the irradiation of the near-field light becomes deficient, thereby it becomes difficult to write information effectively.